Chlamydospore Formation of Fusarium in a Mineral Salt Solution

Abstract

Washed mycelia of Fusarium oxysporum f. raphani seeded in mineral salt solution produced chlamydospores within 24 to 48 hours and the number increased gradually. Initial chlamydospore formation delayed slightly in the mineral salt solution supplemented with 0.1% glucose, but the number increased rapidly thereafter. In 144 hours, production of chlamydospores reached stationary phase and the number formed in water remained about 60% as many as that in the mineral salt solution. Mycelial growth was always observed prior to chlamydospore formation in these media. Glucose was shown to promote mycelial growth and repress chlamydospore formation. Nevertheless, at the stationary phase the number of chlamydospores was increased proportionally to the amount of glucose added into the medium and of the mycelia seeded. Production of chlamydospores in the medium was repressed in the pH below 4 or above 8, and also repressed in CO2 and in N2 atmosphere. Chlamydospore formation was best at 28°C as well as mycelial growth, but in higher temperatures it was more sensitive than mycelial growth. The mineral salt solution lacking one of the elements repressed the production of chlamydospores moderately or completely as a result of repression of the mycelial growth.From these results, it is suggested that the fungus does mycelial growth as much as possible, utilizing the carbon source in the medium and in the mycelium itself, followed by chlamydospore formation from the mycelium at the definite rate.